Whole grains Whole grain foods are underappreciated as a source of antioxidants, say researchers, who conclude a bowl of cereal a day could stave off chronic diseases such as diabetes and heart disease.

"Whole grains are those in which the bran, germ and starch are present in the proportions in the naturally harvested grain," says Lillioja, an endocrinologist, with expertise in type 2 diabetes.

Lillioja says consumption of whole grain food has long been touted as an important way to lower the risk of type 2 diabetes, coronary heart disease and hypertension.

But, he says, to date there has been surprisingly little clear evidence on how much whole grain needs to be eaten daily to achieve these benefits, and what exactly gives whole grain food these benefits.

To investigate these questions, Lillioja and colleagues analysed 11 major prospective studies on the effect of whole grain consumption. The studies involved hundreds of thousands of people in the US, followed for more than a decade.

The review found that those who consumed the maximum amount of whole grains - between 40 and 50 grams - got the maximum protective effect from chronic diseases.

"Roughly speaking, a large bowl of cereal is in the realm of 45 grams [dry-weight] of whole grains," says Lillioja.

But the analysis found that 80 per cent of people studied were not consuming this amount of whole grain.

Lillioja says the benefits of whole grains might be even higher if people consume greater amounts of them.

Bran's hidden value

The new study also highlights what Lillioja says is an overlooked beneficial component of whole grains.

Lillioja says there is a "massive drop" in nutrients when the germ and bran are removed from grains, but the literature to date has been unclear as to why this is the case.

The lion's share of these discarded parts of the whole grain is the bran, which is well known to be beneficial because it contains indigestible fibre, or roughage, which is good for the colon.

But, says Lillioja, only 50 per cent of bran is woody, and the rest is made up of the nutrient-rich aleurone.

"This layer of cells contains all the critical ingredients to get the grain embryo going by dissolving the starch. It's kind of like a storage layer for all the best goodies," he says.

Lillioja says aleurone contains vitamins, minerals, proteins and the antioxidant ferulic acid, which he and colleagues speculate could play a role in preventing the development of chronic disease.

"Everyone thinks bran is just wood, but it's actually as good an antioxidant food as fruit and vegetables," he says.

Whole grain foods include oats and other whole grain breakfast cereals, brown rice and bread made from wholemeal flour.

But Lillioja says current packaging makes it hard to tell how much whole grain is in each food.